1. Field of the Invention
The invention relates to a method of providing filtration of contaminants from process streams. More specifically, the invention relates to a method of providing filtration of contaminants from process streams upstream of process units.
2. Description of Related Art
Refineries, petrochemical plants and other similar type plants process large amounts of both liquids and/or vapor phase process streams through a variety of process units. Feed filters and other pre-filter systems, which are also referred to as guard beds or guard filters, are frequently used to remove undesired particulates from the process streams prior to being fed to a process unit. As used herein, these feed filters and pre-filter systems will be referred to as guard filters. Guard filters that are used in adsorption applications can be run at ambient or somewhat elevated temperatures while the downstream process units can run at elevated temperatures, elevated pressures or different atmosphere conditions, such as high hydrogen partial pressures. Guard filters that are used in absorption applications are often run at elevated temperatures, such as in the downstream process units.
Often a filtration system is employed within the actual process unit (in-situ), such as “top bed” materials in a down flow reactor. Guard filters can be used to replace this type of in-situ system. More likely guard filters are used to augment the in-situ system when large volumes of particulates are typically seen that will overwhelm even the most robust of these in-situ process unit systems.
Guard filters can use either a fixed filter system or a deep bed filter system or a combination of the two systems.
Fixed filter systems can include cartridge, bag, canister, belt filters, precoat filters, centrifuges, air filters, dust bag collectors, membrane filters, and other type of filter systems. While high filtration efficiencies can be achieved, the filtration capacity of these fixed filter units is relatively small, which typically requires changing out filter elements or backwashing or otherwise cleaning the filters on a regular and frequent basis. The cost of filtration elements and the cost of the effort to change out or clean these guard filters can be expensive. Sometimes the process stream itself is used to backwash the filtration system, which results in the backwash stream becoming contaminated with particulates and often downgraded in value. It is estimated, for example, that some petroleum refineries incur a downgrade cost of over one million dollars per year to operate a fixed feed filter system on a 40,000 barrel per day hydroprocessing unit. Additionally, if only one fixed feed filter system is used, there is a significant time period during cleaning, backwashing, or filter element replacement when unfiltered feed is fed to the downstream process unit. These periods of unfiltered feed can contribute to pre-mature performance problems in the process unit, which results in more frequent downtime and higher maintenance costs.
Some facilities have employed deep bed filters instead of, or in addition to, fixed filter systems due to their higher capacity. The filter medium in fixed filter systems traps particulates in a very thin layer, i.e., a fraction of an inch, on the surface of the filter element. Deep bed filters effectively filter to a depth of inches. The media in deep bed filters have typically been sand, gravel, catalyst, spent catalyst, off spec catalyst, regenerated catalyst, catalyst carriers, ceramic rings, and combinations thereof.
Shortcomings of conventional guard filters include clogging of the filter medium, the limited capacity of the filter medium to remove particulates, the inability of deep bed filter media to trap particles less than about 25 microns in size, and inability of many fixed filter media to withstand elevated temperatures when required.
In conventional guard filters, the filter medium eventually clogs or blocks flow through the filter medium. When the filter medium clogs, the flow rate of the stream through the filter medium drops and the pressure drop across the guard filter rises eventually to unacceptable levels at which point the guard filter must be taken off-line for filter media replacement or cleaning.
Conventional filter media have limited capacity to remove particulates. Cartridge, bag, and mesh filters fill their void spaces quickly and must be replaced or cleaned frequently. Conventional deep bed filters can have a greater capacity but experience shows that such systems have the ability to trap particulates in only the top six to twelve inches of the bed. It is this layer that clogs first as the particulates fill the void spaces through which the process stream is trying to flow. This produces an impenetrable cake of particulates and causes the filter system pressure drop to eventually rise to unacceptable levels.
Contaminants in process streams can be deleterious to processes and also to process units. Contaminants can damage process units, potentially resulting in an environmental or safety incident. Contaminants can also damage processes by decreasing efficiencies within processes, deactivating or poisoning catalysts, reducing the yield of desired products, reducing the conversion rates of desired components, increasing the rate of generation of undesired products, stopping production, affecting the specifications of products, or the like. Contaminants can be found in all types of process streams, such as feed streams, recycle streams, discharge streams, or effluent streams. Contaminants can affect various types of process units, such as reactors, extractors, distillation columns, scrubbers, tail gas treaters, incinerators, tanks, vessels, heat exchangers, furnaces, packaging facilities, pipelines, catalytic process units, extractors, scrubbers, boilers, condensers, and the like.
It is highly desirable to have filter media that do not clog with contaminants, but efficiently and effectively filter contaminants from the process stream. Efficiency relates to the percent of contaminants removed by such filter media from the process stream, as well as, to the range of sizes of contaminants that can be removed by such filter media. Effectiveness relates to the extent that such media does not impede the flow of the decontaminated process stream through the media. Such media would desirably remove essentially all contaminants within a broad range of sizes from the process stream, while not causing an unacceptable pressure drop increase across the guard filter. The method of the present invention for filtration for process streams, when compared with previously proposed prior art methods, has the advantages of providing highly efficient and highly effective filtering of contaminants.
Disadvantages associated with current perpendicular flow distribution designs and methods in deep bed filter units can result in poor distribution within the guard filter. Clogging or other fouling, such as that caused by particulate contaminants or the products of undesired polymerization reactions, may also cause maldistribution. The maldistribution may result in channeling and corresponding bypassing of portions of the filter media, reduction in the efficiency of contaminant removal, and reduction in efficiency of the guard filter. Therefore, the art has sought a perpendicular flow distribution method that can distribute the process stream more uniformly within the guard filter, provide efficient filtering of contaminants, and reduce fouling caused by undesired polymerization reactions.
It has been proposed to use reticulated ceramic materials to filter and distribute organic feed streams in a chemical reactor. A need exists for improved filtering and flow distribution capabilities for other types of process streams besides organic-based streams and for guard filters, not just chemical reactors.
There is also a need for an improved guard filter that avoids or minimizes the shortcomings associated with conventional guard filters, such as high operating costs and limited filtering capabilities.